JEE MAIN - Mathematics (2023 - 24th January Morning Shift - No. 7)
Let $$\Omega$$ be the sample space and $$\mathrm{A \subseteq \Omega}$$ be an event.
Given below are two statements :
(S1) : If P(A) = 0, then A = $$\phi$$
(S2) : If P(A) = 1, then A = $$\Omega$$
Then :
both (S1) and (S2) are true
both (S1) and (S2) are false
only (S2) is true
only (S1) is true
Explanation
$\Omega=$ sample space
$\mathrm{A}=$ be an event
$ \Omega$ = A wire of length 1 which starts at point 0 and ends at point 1 on the coordinate axis = $[0,1]$
$\mathrm{A}=\left\{\frac{1}{2}\right\}$ = Selecting a point on the wire which is at $\left\{\frac{1} {2}\right\}$ or 0.5
As wire is an 1-D object so from geometrical probability
$P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
Here total length of wire = 1 unit
and point has zero length so point A at $\left\{\frac{1} {2}\right\}$ or 0.5 has length = 0.
$$ \therefore $$ Favorable length = 0
$$ \therefore $$ $\mathrm{P}(\mathrm{A})=0 {\text { but }} \mathrm{A} \neq \phi$
Now $\overline{\mathrm{A}}$ = $[0,1]$ - $\left\{\frac{1} {2}\right\}$
So, length of $\overline{\mathrm{A}}$ = Length of entire wire - Length of point A = 1
$$ \therefore $$ $\mathrm{P}(\overline{\mathrm{A}})=1 {\text { but }} \overline{\mathrm{A}} \neq \Omega$.
Then both statements are false.
Attention : According to NTA option A is correct. Which is wrong. That is proven here using geometrical probability.
Note :
Geometrical probability :
1. For 1-D object, $P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
2. For 2-D object, $P(A)=\frac{\text { Favourable Area }}{\text { Total Area }}$
3. For 2-D object, $P(A)=\frac{\text { Favourable volume }}{\text { Total volume }}$
$\mathrm{A}=$ be an event
$ \Omega$ = A wire of length 1 which starts at point 0 and ends at point 1 on the coordinate axis = $[0,1]$
$\mathrm{A}=\left\{\frac{1}{2}\right\}$ = Selecting a point on the wire which is at $\left\{\frac{1} {2}\right\}$ or 0.5
As wire is an 1-D object so from geometrical probability
$P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
Here total length of wire = 1 unit
and point has zero length so point A at $\left\{\frac{1} {2}\right\}$ or 0.5 has length = 0.
$$ \therefore $$ Favorable length = 0
$$ \therefore $$ $\mathrm{P}(\mathrm{A})=0 {\text { but }} \mathrm{A} \neq \phi$
Now $\overline{\mathrm{A}}$ = $[0,1]$ - $\left\{\frac{1} {2}\right\}$
So, length of $\overline{\mathrm{A}}$ = Length of entire wire - Length of point A = 1
$$ \therefore $$ $\mathrm{P}(\overline{\mathrm{A}})=1 {\text { but }} \overline{\mathrm{A}} \neq \Omega$.
Then both statements are false.
Attention : According to NTA option A is correct. Which is wrong. That is proven here using geometrical probability.
Note :
Geometrical probability :
1. For 1-D object, $P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
2. For 2-D object, $P(A)=\frac{\text { Favourable Area }}{\text { Total Area }}$
3. For 2-D object, $P(A)=\frac{\text { Favourable volume }}{\text { Total volume }}$
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